This is a widespread species with a strong dependency on corals that have undergone widespread population declines ranging from 20 to 37% because of coral reef loss. It has been eliminated on reefs that undergo massive bleaching events. Chaetodon trifascialis has a strong dependency on a species of coral (Acropora hyacinthus) that is listed as Near Threatened and although it has been seen to feed on at least 14 other coral species variously listed as Least Concern (seven species), Near Threatened (six species) and Vulnerable (one species), all of these corals have shown substantial population declines because of coral reef loss throughout the Indo-Pacific. We infer that population declines of C. trifascialis are similar to those of A. hyacinthus (and other species it feeds on) and therefore list this species as Near Threatened (nearly meeting VU A3ce with an estimated generation length of between six and seven years).

This species is very widespread throughout the Indo-west and central Pacific, from the Red Sea to the Society Islands. North to southern Japan, and south to Lord Howe Island and Rapa (Pyle 2001, G.R. Allen pers. comm. 2006). It has been recorded as a vagrant from the Hawaiian Islands. The range size is ~76.2 million km2, from values estimated by Jones et al. (2002) based on projections of distribution maps from Allen et al. (1998). It is found at depths of 2-30 m.

It is generally common (e.g., mean of 0.66 individuals per 200 m2 in northern Great Barrier Reef; Pratchett and Berumen 2008), but very vulnerable to changes in the abundance of its preferred coral prey, tabular Acropora (Berumen and Pratchett 2006, Pratchett et al. 2006). It went locally extinct (100% decline in abundance) before and after a severe bleaching event (90% coral loss) in the central Great Barrier Reef (Pratchett et al. 2006). The abundance and persistence of this species is highly linked to Acropora corals (including A. hyacinthus and A. cytherea). The declines of these coral species can be used as a proxy for declines in abundance of C. trifascialis.

There appear to be no species-specific conservation measures in place. This species is present within marine protected areas. Monitoring of this species is needed in conjunction with coral monitoring, as well as determination of the degree of co-dependence between this species and corals.

Reese, E.S. 1981. Predation on corals by fishes of the family Chaetodontidae: implications for conservation and management of coral reef ecosystems. Second International Symposium on Biology and Management of Tropical Shallow Water Communities (coral reefs, bays and estuaries), 20 July - 2 August 1980: 594-604.. Papua New Guinea.